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The question and answer are correct. I think we should all know this. I am presenting a set of facts -- In my opinion, there are two solutions for solving the schemas issues -- (1) Use deterministic content models such as DTD or XML Schemas (2) Use non-deterministic content models as in RELAX or TREX. Tentatively, deterministic content models are easier for specifying key constraints, but I think document processing (such as XSLT or Query) gets *very* ugly. Non-deterministic content models are very clean for document processing, but we have to do *small* (note the emphasis on small) tricks to support key constraints -- I think I can say that RELAX group has people who very actively work on this. Also, if you look at TREX's goal, it says non-deterministic content models are almost necessary and definitely convenient for several use cases. I should say this -- I believe *very* strongly in non-deterministic content models, and I think that is the way document processing can be supported neatly. So I am *very* biased, and I use RELAX for my purposes - and not XML Schema. Actually I think I cannot afford to use XML Schema. If you want to know more about deterministic content models, you should read Appendix E of XML 1.0, it is very good. Also, I think I am right when I say that Anne Bruggemann Klein is the first person to analyze these deterministic content models as in DTDs, but she also opines that deterministic content models are *very* restrictive and is not the way it should be. I also heard this: XML Schema WG has discussed deterministic content models a lot, and they decided to use deterministic content models largely for parser simplicity -- which I think is a non-valid reason at this point. In short, I do not know why XML Schema:Structures is becoming a standard in the first place. <warning>speaking for himself only</warning> regards - murali. On Tue, 17 Apr 2001, Marcus Carr wrote: > > Anshul.Mittal@i... wrote: > > > I have a requirement where I have to specify the following condition > in a dtd... > > ecat-supp-name and ecat-supp-code are individually > optional but one of the > two needs to be present to locate the vendor > > > So I need to have ecat-supp-name or ecat-supp-code or or both in > the higher > level element... > > Thats how I wrote the dtd . > > > <!ELEMENT LineItem > (((EcatSuppName|EcatSuppCode)|(EcatSuppName,EcatSuppCode)), > ((EcatSuppPartNbr|EcatSuppModel)|(EcatSuppPartNbr,EcatSuppModel)), > ManufacturerName?, EcatItemDesc, CommCodeXref?, EcatQuantity, > EcatUom, EcatUnitPriceFx, EcatCurrency, EcatCatalogId?, > EcatPONumber?) But getting the following error " Content Model is > non - deterministic for LineItem" when I try to validate this dtd. > > The problem is that the processor can't determine where it is when it > encounters the EcatSuppName element, because it doesn't know if it > requires an EcatSuppCode to follow or not. Even if you got past this > problem for this set of elements, it would recur when the processor > got to the EcatSuppPartNbr in the same content model. The following > model allows either or both elements in the set to occur and requires > one as the minimum. The only restriction is that if both elements in > the set exist, they must be in a fixed order, but that restriction is > present in your current model anyway. > > <!ELEMENT LineItem (((EcatSuppName, EcatSuppCode?) | (EcatSuppCode)), > ((EcatSuppPartNbr, EcatSuppModel?) | (EcatSuppModel)), > ManufacturerName?, EcatItemDesc, CommCodeXref?, > EcatQuantity, EcatUom, EcatUnitPriceFx, EcatCurrency, > EcatCatalogId?, EcatPONumber?)> > > > Any Idias ?? > > Extending Easter holidays for another week? :-) > > > -- > Regards, > > Marcus Carr email: mrc@a... > ___________________________________________________________________ > Allette Systems (Australia) www: http://www.allette.com.au > ___________________________________________________________________ > "Everything should be made as simple as possible, but not simpler." > - Einstein > > > > ------------------------------------------------------------------ > The xml-dev list is sponsored by XML.org, an initiative of OASIS > <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To unsubscribe from this elist send a message with the single word > "unsubscribe" in the body to: xml-dev-request@l... >
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